Power generation continues to be an important application of rotating electrical machines. Wind energy is one of the fastest growing sources of electricity in the United States and around the world, and wind turbines employing rotating electrical machines are used to convert wind energy to usable power. The generator component of a wind turbine includes the electrical generator, control electronics, and an optional gearbox for converting the low speed incoming rotation to high speed rotation suitable for generating electricity. In a wind turbine, the generator component may be approximately one third of the overall wind turbine cost.
In some conventional non-superconducting generators, stator windings are surrounded by a back iron that acts as a magnetic flux path. The back iron is often in the form of stacked laminated plates, the plates including iron teeth that extend between the stator windings to provide a flux path and to support the stator windings, which are positioned in slots formed between the teeth. In such machines, which often operate at high frequencies of 60 Hz or greater, the teeth carry the magnetic flux, and the ratio of the area of slots to the area of teeth is about 50 percent. This ratio is required in conventional machines to accommodate the magnetic flux generated in these machines. In some conventional machines, tooth area is actually increased relative to slot area as a means to reduce the cost of the machine, due to relative differences in cost between iron and copper.
Superconducting generators have been under development since the early 1960s. The use of superconducting windings in these machines has resulted in a significant increase in the magnetomotive forces generated by the windings and increased flux densities in the machines. The flux densities were increased to such an extent that there were high losses due to saturation of the iron teeth, as well as due to eddy current losses. As a result, superconducting machines have been developed to operate without iron teeth between the stator coils since the flux density would result in high dissipation in these members. In some cases, fiber-composite teeth, rather than iron teeth, are used to support stator coils in these machines. However, such fiber composite teeth are very expensive to manufacture.